If you have a string instrument of any kind that needs fixing, a mistake you made in building a new instrument that you need to "disappear," or a question about the ethics of altering an older instrument, ask here. Please note that it will be much easier for us to help you decide on the best repair method if you post some pictures of the problem.

So, I was at a buddy's house last night when his son came home and showed us the damage. I don't know the model for sure, but I think it's probably a DX1AE. Anyway, he had performed at school and in the meantime left the guitar unattended. It looks like it fell. Strangely, no one saw what happened.
So, here's the deal... It's a spruce top/HPL back and sides Martin. The damage is on the back lower bout. The impact caused the HPL back to separate from the sides exposing the kerfing (which is still intact.) Gluing the back plate back down would be simple enough, assuming I knew the best adhesive to use on HPL, but the bigger problems is that it also took a big chip out of the back along the edge (about half the size of a dime.) I assume the chip was lost, but maybe he thought to find it and save it... probably not.
I've never done this kind of work on an HPL guitar. I guess a person could use CA?
What about the big chip? If it was wood I could just patch it. As it is, I don't have any mahogany figured HPL laying around my shop.
I thought about seeing if he would let me put a binding on it (I've always hated that it didn't have any bindings anyway.) That could cover a lot of the damage. (and IMO probably would have helped reduce the extent of the damage in the first place.)
I'll see if I can get back over there later to take a few pics to post on here.
What would you guys do? thanks

First, I wouldn't spend much time on it because I have worked on a lot of those guitars and I just don't think much of them myself.
However...fix it and get it back to him so he can keep playing! I would use epoxy, or thick CA to glue the laminate. i think that you could also use wood glue but I'd play it safe with one of the others. Epoxy works well here because it fills gaps and is very easy to clean up with alcohol, which doesn't hurt the finish on the laminate at all.
If you don't have the missing chip, you'll just have to patch it up the best that you can! As far as adding binding, I think that would take a lot of time and probably not be worth it.

Mark. Thanks for the tip on the thick CA. I was thinking of using medium... probably too thin... I do like the epoxy idea because of it's ability to fill gaps. And yes I absolutely agree that putting binding on it would not be worth it and I would not do it most of the time. but he's a really good friend of mine (and the drummer in my band) and I would only do it as a labor of love anyway.

I don't know if a picture was necessary here.. but everyone likes a picture...

you can see the kerfing exposed.. he's currently holding the back on with scotch tape
it's separated probably about 8 inches along the back/side joint.

I ordered a sample of honduran mahogany laminate form wilsonart. I know it's not the same thing, but I figured it was worth checking out. you can order online and they will send you a free sample with no shipping charges.

First of all, I believe HPL = 'high pressure laminate'. (That's mostly for those reading and scratching their heads wondering what HPL means.)
Martin used superglue (CA, cyanoacrylate) for those "Formica" guitars, and they can also supply you with little "samples" of material from which to try to pick a match for patching (you might have to be a Martin authorized warranty center to get those). I'd chalk fit and superglue a matching patch into the chip.

I did a similar repair on an ovation that suffered a similar fate and used epoxy (System 3) and it worked out fine. I was able to clean up any squeeze out with alcohol as I went along and used binding tape to hold it all together.

Adding binding to an HPL guitar can be difficult to do. The color coat is very thin so scraping to level the bindings can expose the substrate, which is a uniform dull brown. Also if you use the wrong bit routing the rebate you can "blow out" chunks of the side, which are much harder to repair than wood would be.
If you take the guitar to a kitchen remodeler or a cabinet shop they usually have laminate sample boards from which you may be able to find a matching "chip" . The chips are about 1 1/2 " X 2" and are given away for free so people can compare a sample of the laminate to their cabinets or other decor. If you explain what you need most of these people will be willing to help. You will find many different "mahoganys" and "cherrys" from different manufacturers to choose from.
There are professional touch up people who repair scratches and chips in laminate countertops so they are virtually undetectable. It is a skill learned through practice. The cost of repairing a "little scratch" often reflects this rather than the actual work involved.

I remember those laminate samples from my cabinet shop days. If you go to a cabinet shop and get laminate samples, go ahead and get plenty of them if they will give them to you, and keep them in your shop. They make great scrapers, spreaders, shims, and other shop tools. It's hard to find a better "tool" for spreading pore filler.

He actually was able to save the piece that chipped out and it's in pretty good shape, considering. I think it'll turn out to be a pretty easy fix. He's not going to want to pay to have Martin replace the back. There will just have to be a permanent battle scar. adds character anyway. I also just noticed that it also made a crack in the top. it's a tight crack and will probably disappear when I'm done with it.
Thanks to all of you for your suggestions, especially on acquiring patch material. though I probably won't be needing it now it's still good for future reference.
And I've pretty much all but talked myself out of the binding idea... I just really hate seeing it without.. To me it just makes it look cheap and vulnerable. I don't think the crack on the top would have even happened if it had a binding, and I'm sure the damage on the back would have been much less severe... Besides the fact that the spruce top is all dented and dinged up all around the edges. I know you can't really do much scraping around HPL, I was just figuring it would have to be a one-shot deal... get it as close as you can the first time and call it done.